1. Field of the Invention
The present invention relates to an inkjet recorder and particularly to technology for further reapplying ink (for example, ultraviolet curable ink) to a paper surface on which an image is formed by digital printing, offset printing, etc.
2. Description of the Related Art
Technology referred to as so-called overcoating is a known ink jet recorder printing technology. In overcoating, a sheet of paper on which an image has been formed beforehand is thickened around the, e.g., text of the image, the sheet of paper is made to be partially glossy, a three-dimensional impression is made on the sheet of paper, and/or a complicated color expression is achieved by printing one color on top of another on the sheet of paper. For example, a transparent ink is printed over a base print so as to produce a three-dimensional effect, or ink that is different in color and in property is overprinted in accordance with the color of a printed image serving as the base print so as to darken the printing color or to express color that cannot be expressed by only carrying out printing once. As an example of this, there is a case where, for example, after an image is formed on a paper surface by digital printing, offset printing, etc., an ultraviolet curable ink (hereinafter, referred to as “UV ink”) is applied in a thick layer over the image, and an ultraviolet ray is radiated so as to cure the ink (spot UV printing) (see, for example, Japanese Patent Application Publication No. 2009-255572). In order to produce a three-dimensional effect using a printed image that serves as a base print, a transparent UV ink is widely used as an UV ink.
Overcoating is performed for the purpose of, e.g., decorating an image on a sheet of paper that has already been printed. Thus, an ink layer for the overcoating needs to be accurately formed at the position matching up with the printed image. Therefore, conventionally, a mark (hereinafter, referred to as a “registration mark”) for positioning is printed, in advance, at the periphery of a printing area at an end portion of a sheet of paper, and the position of a printed image may be identified with reference to the position of the registration mark. From this, a position may be set for discharging ink for the overcoating. Even when there is a misalignment in the printed image, the discharge position is corrected with reference to the position of the registration mark. More specifically, a technique has been employed where a pair of registration marks is printed along the width of the front end of a paper surface in the direction of conveyance of the sheet of paper.